**3. Types of flexor tendon injury**

#### **3.1. Patterns of injury**

A sharp laceration to a flexor tendon is the most common cause of injury (for example from a knife or glass). It is rare for blunt injuries to divide the tendon but the significant crushing to the tendon can result in adhesions if not managed properly. Avulsion injuries are also common.

**4. Tendon healing and latest molecular updates**

**Table 1.** Modified Leddy and Packer classification for FDP avulsion [9–11].

Type I FDP and both vincula rupture with no fractures

Type II FDP ruptures but long vincula remains intact

*Early operative repair necessary*

Avulsed FDP held at PIP joint

*Repair required within 3 months* Type III FDP avulsion with a large bony fragment that gets caught at A4 Both vincula are preserved *No time limit for repair*

phalanx (extra-articular)

phalanx (intra-articular)

here may be a small avulsed bony fragment

Type IV FDP and bony fragment avulsion, with tendon avulsion from the bony fragment Type Va FDP and bony fragment avulsion, in association with fracture of the distal

Type Vb FDP and bony fragment avulsion, in association with fracture of the distal

tor (VEGF), help initiate the vascular invasion to the site of injury [13].

that adhesions between the tendon and its sheath become more apparent

**4.1. Intrinsic healing**

Tendon healing undergoes overlapping inflammation, proliferation and remodelling [12] via two mechanisms -extrinsic and intrinsic [7]. Within the first week of injury, blood vessels within the tendon and tendon sheath form a thrombus at the injury site which acts to recruit vasodilators and proinflammatory cells [12]. These cells migrate to the injury site and help with removal of necrotic tissue, fibrin, clot and cellular debris through phagocytosis. Canine models have shown that angiogenic factors, such as vascular endothelial growth fac-

Tendon retracts into palm, presenting as a tender lump

Flexor Tendon Injuries

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http://dx.doi.org/10.5772/intechopen.73392

In the third week, the tendon enters the proliferative stage whereby the fibroblasts rapidly proliferate, synthesis immature collagen in an unorganised manner, and assist with the production of extracellular matrix (ECM) [14]. This initial laid down collagen is type III collagen which is a weaker form of the type I collagen present in native tendons. The combination of type III collagen and previously initiated vascular network leads to scar formation within the tendon- this initially decreases its strength before the tendon enters the final stage of healing At weeks six to eight, the remodelling stage predominates. Here type I collagen fibres are reorganised in a longitudinal manner along the long axis of the tendon with collagen fibrils crosslinking to one another to increase the strength of the tendon [14]. It is during this stage

Intrinsic healing involves only the tenocytes (fibroblasts) within the tendon itself and depends on the migration and proliferation of cells from the epitenon and endotenon [7, 14]. Epitenon

#### **3.2. Lacerations**

Lacerations may be complete or partial [2]. Lacerations within Zone 1 only involve FDP and those in Zone 2 usually involve both FDP and FDS tendons as well as any neuromuscular injury. Tears within the fibro-osseous sheath are more prone to restrictive adhesions than those within Zones 3–5. However, small lacerations in Zones 3–5 frequently involve multiple tendons and major neuromuscular structures

#### **3.3. Avulsion injuries**

Four factors determine the prognosis of avulsion injuries of flexor tendons: the extent of retraction of the proximal tendon, the remaining blood supply, the time interval between trauma and surgery, and the presence and size of any osseous fragments [2].

The FDP tendon is prone to avulsing from its insertion into the distal phalanx and is commonly called a "jersey injury" [9]. This occurs when the distal phalanx is extended at the DIP joint while the FDP is maximally contracted. This avulsion may involve a fragment of bone. Jersey finger most commonly affects the ring finger because it is the most proximal digit when the hand is flexed. Leddy and Packer have classified jersey injuries into Types I to III [9]. This classification has been modified by Smith who added a Type IV injury [10] and Al-Qattan who added Type V [11] (**Table 1**).


**Table 1.** Modified Leddy and Packer classification for FDP avulsion [9–11].
